Stopping Blender seeing all system/network folders in campus/school install
@pluke - These are no vanilla MS product settings, your tech team set those settings via group policies which are part of MS active directory services. 

Blender does not use the operation system's file selection system (or any other default file selection system on other operating systems), thus it doesn't read any of the group policies. 

There is no easy way to do that and more important you'll need administrator rights.